Syringes

ABSTRACT

A syringe has a barrel 1 housing a plunger 8 linked to a piston incorporating a seal 7 by a coupling member 9. A flange 12 on the coupling member 9 limits the extent of movement of the plunger and piston assembly, in association with latches 16. As the plunger 8 is operated through a sequence of expelling air from the syringe, to draw in liquid into the syringe and then to eject the liquid out again through a needle connected to an outlet 5, camways 11 at the ends of the coupling member 9 operate with projecting keys in such a way that the coupling member 9 is caused to rotate in stages. Then after the plunger is withdrawn again (after ejection of the liquid) the projecting keys 10 on the part associated with the piston seal 7 will become detached from the relevant keyways 11 so that the syringe cannot be used a second time.

This invention relates to syringes and in particular to so-calleddisposable syringes, which are used in general medical practice as aneffective way of preventing cross-infection. However, due to shortagesof these products, and possibly ignorance, there is a tendency,particularly in the Third World, to use the syringe maybe five or sixtimes before throwing it away. Drug users also commonly share syringes,which are used many times, because they do not have access to a regularsupply.

It is an object of this invention to provide a disposable syringe whichis effective in operation, can be used in a conventional manner, ischeap to produce and will deter attempts to reuse the syringe.

According to the invention there is provided a syringe comprising abarrel housing both a piston and a plunger for moving the piston toenable a liquid to be drawn in to and ejected from a portion of thebarrel, the piston and plunger being interconnected by a decouplinglinkage such that the plunger is operatively disconnected from thepiston after the plunger has been retracted and subsequently depressed.

In the preferred arrangement the piston and the plunger areinterconnected by a coupling member. In this case the coupling membermay be interconnected to both the piston and the plunger by a decouplinglinkage. Ideally the piston or the coupling member carries a flangewhich interacts with latches on the inner wall of the barrel so as to beable to pass the latches before disconnection of the or each decouplinglinkage but is unable to pass the latches upon attempted withdrawal ofthe plunger after such disconnection. The latches may, for example, bein the form of inwardly projecting serrated ribs on inwardlysprung-loaded arms. Preferably, the flange will incorporate keywayswhich can ride up the latches whilst the flange is in one rotationalattitude, the latches abutting the flange when the flange is inalternative rotational attitudes. In this case the or each decouplinglinkage will ideally be effective to cause rotation of the part carryingthe flange upon application of reciprocation movements to the plunger.It will be understood that any connection means which fulfils thisfunction is applicable. For example, the or each decoupling linkage maybe threadedly engaged and the piston may be interconnected with thebarrel of the syringe so that it is caused to rotate during axialmovement, the threaded engagement being such that on a second retractionof the plunger the piston and plunger become disengaged.

In the preferred embodiment the or each decoupling linkage includes acamway on one part for receiving a cam follower on the other part, thecamway being shaped such that movement of the plunger causes relativemovement between the cam follower and the camway, whereby the camfollower is removed from the camway on a second retraction of theplunger.

The cam followers may, for example, be diametrically opposed pins,locating in a ring having the camway formed on an inner surface. Thesepins may, with advantage be positioned at the ends of fingers which areflexible but biased in the axial position of the piston, so that thepins will be biased to follow the camways in one direction only.Additionally the pins may carry projecting webs which resist movement ofthe pins in the other direction through the camway.

If desired the parts of the or each decoupling linkage defining thecamway and the cam follower respectively may be biased apart by a springor other biasing means.

The plunger and piston may be keyed together for rotational movement butseparable on retraction after disconnection of the decoupling linkage.The syringe may include one or more cover plates for preventing accessto the decoupling linkage after operative disconnection of the pistonand plunger. Where the plunger can be full withdrawn from the syringe itmay be hollow so that it can be used as a needle cover to preventinfection spreading, due to accidental scratches during subsequenthandling.

The mechanism employed in the syringes of this invention is such thatthe syringe can be handled and operated in the conventional manner,without any additional special movements, in order to deliver aninjection satisfactorily and in accordance with correct practice.

The invention may be performed in various ways and preferred embodimentsthereof will now be described with reference to the accompanyingdrawings, in which:

FIG. 1 is a vertical section through one embodiment of an assembledsyringe of this invention;

FIGS. 2A, 2B and 2C are respectively a vertical section, a side view anda a top view of a syringe barrel of the syringe shown in FIG. 1;

FIGS. 3A, 3B and 3C are respectively side views and sections on linesA--A and B--B of the plunger and piston unit of the syringe of FIG. 1;

FIGS. 4A to 4E illustrate various stages of operation of the syringeshown in FIG. 1;

FIG. 5 shows a modification to the design of the plunger and piston unitof the syringe shown in FIG. 1;

FIGS. 6A and 6B are a vertical section and a top view respectively of amodified barrel for the syringe shown in FIG. 1;

FIGS. 7A and 7B show, in perspective and side view respectively; analternative type of coupling arrangement for the plunger and piston unitof the syringe shown in FIG. 1;

FIGS. 8A to 8F illustrate stages of operation of the couplingarrangement shown in FIG. 7;

FIGS. 9A to 9F show comparable stages of operation of a modified form ofcoupling arrangement, whilst FIG. 9G shows the modification on a largerscale; and

FIG. 10 illustrates a further modification to the coupling arrangementshown in FIG. 7.

Referring now to FIGS. 1 to 3, the preferred form of syringe comprises asyringe barrel 1 enclosing a plunger and piston unit 2. The barrel 1 hasan upper plunger housing 3 and a lower piston housing 4 leading to anoutlet 5 which will receive the syringe needle. The unit 2 has, at itslower end, a seal mount 6 carrying a piston seal 7. The mount 6 islinked to a plunger 8 by a coupling 9. The interconnection of thecoupling 9 to the mount 6 and the plunger 8 is achieved by means of apair of projecting keys 10 on those two parts received within camways 11at the two ends of the coupling 9.

The coupling 9 also incorporates a flange 12 provided with a pair ofkeyways 13. The plunger 8 incorporates a pair of tracks 14 formed downthe sides which engage with ribs 15 projecting in from the side walls ofthe plunger housing 3 which ensures that the plunger does not rotate asit is raised and lowered within the plunger housing 3. The plungerhousing 3 also incorporates inwardly biased sprung latches 16 which willfit within the keyways 13 of the flange 12 on the coupling 9. Thelatches 16 can be forced apart by the portion of the flange 12 ofgreater diameter but will snap inwardly above the larger diameterportion of the flange 12 once the flange has been moved below thelatches.

Use of the syringe is illustrated in FIG. 4. The completely assembledplunger and piston unit 2 will be introduced into the barrel 1, with thetracks 14 sliding down the ribs 15, as shown in FIG. 4A. The keys 10 aremanufactured with thin connecting pieces which attach the keys to theends of the coupling 9 and when the plunger 8 is pushed fully home,these connecting pieces will shear so that the keys 10 enter the camways11, as shown in FIG. 4B.

Retraction of the plunger 8 (FIG. 4C) causes the keys 10 to enter intosubsequent sections of the camways 11 which forces the coupling 9 torotate into a condition wherein the keyways 13 on the flange 12 arealigned with the latches 16. Further withdrawal of the plunger 8 causesthe flange 12 to ride up the latches 16 until the flange 12 enters theupper portion of the plunger housing 3 of largest internal diameterwhere the flange 12 is freely rotatable (FIG. 4D).

Finally, depression of the plunger 8, causes the keys to move intofurther sections of the camways 11 resulting in further rotation of thecoupling 9 (FIG. 4E). This also results in ejection of a dose drawn intothe piston housing 4 during the previous stage, and in the flange 12being forced past the spring-like latches 16. Any attempt to withdrawthe plunger 8 (by more than a fairly small amount) will be defeatedsince the flange 12 will now abut against the latches 16 and cannot passthese latches because the keyways 13 in the flange have been rotated outof alignment with the latches 16.

It will be appreciated that during the steps illustrated in FIGS. 4A to4E, air will be expelled from the syringe, the required dose will bedrawn into the piston housing 4 and will then be ejected through theneedle attached to the outlet 5 upon final depression of the plunger 8.Further use of the syringe is prevented because the coupling 9 cannotagain be withdrawn within the plunger housing 3, and in any case isdecoupled from the piston seal 7.

FIG. 5 illustrates the incorporation of spring members 17 (which can beformed as part of the original moulding) which bias the seal mount 6 andthe plunger 8 away from the coupling 9. These springs 17 ensure that thekeys 10 follow the paths through the camways 11 if the piston housing 4is filled with a dose by means of pressure from a pressurised vial,rather than by pulling on the plunger 8. Again, however, in the initialstage, the plunger and piston unit 2 will be introduced into the barrel1 and pressed fully home so as to shear the connecting pieces betweenthe keys 10 and the ends of the coupling 9.

FIGS. 6A and 6B illustrate a modified form of barrel wherein the latches16 are replaced by serrated keys 18. Once the plunger 8 has beenwithdrawn into the condition illustrated in FIG. 4D subsequentdepression of the plunger 8 will cause the flange 12 to move past theserrations in the keys 18 in the manner of a ratchet type mechanism.This prevents the unethical user from delivering reduced doses ofvaccine by attempting to avoid full operation of the latches as in thetype of syringe construction illustrated in FIG. 1. As an alternative,modified forms of latches could be provided to overcome this problem.

An alternative type of coupling arrangement is illustrated in FIGS. 7Aand 7B. Here each key 10 is carried at the end of a spring sectionfinger 19. There is a single key 10 for each part 6 or 8. Again, duringinitial manufacture the keys 10 are attached to parts of the coupling 9by thin connecting pieces, namely at the point 20. The shape of thecamway 11 can be seen clearly from FIG. 7.

FIG. 8 shows the stages of movement of the keys 10 through the camway 11as the plunger 8 is pushed in and out for the necessary filling andinjection of the required dose. As the plunger 8 is pushed downwardlythe finger 19 is bent into the position shown in FIG. 8A and is thussprung loaded. Further downward pressure of the plunger causes the thinconnecting piece to break so that the key 10 drops down the firstvertical portion of the camway 11, as shown in FIG. 8B. Withdrawal ofthe plunger then results in the sprung loaded finger 19 moving up theangled portion of the camway 11 (FIG. 8C). This is the condition of thesyringe as supplied from the manufacturers to the end user.

Depression of the plunger 8 now causes the key 10 to drop into the lowercentral portion of the camway 11 (FIG. 8D). This causes air to beexpelled from the piston housing 4. The plunger is then withdrawn tocause the dose to be drawn back into the piston housing 4 and the key 10moves upwardly again and across to the position shown in FIG. 8E.Finally, operation of the syringe to expel the dose causes the key 10 tomove into the final portion of the camway 11, where it is free to becomereleased from the coupling 9 should the plunger 8 be withdrawn again.Consequently the piston 7 cannot again be withdrawn.

A slight modification of the arrangement shown in FIG. 7 is illustratedin FIG. 9. As can be seen from FIG. 9G at the end of the finger 19,adjacent to where the key 10 projects, there are provided two projectingwebs 21. Both prior to and at the end of a complete operating cycle, oneor other of these webs 21 projects and engages with latches 16 (FIG. 2)or serrated keys 8 (FIG. 6). Such webs 10 could also engage withinradial grooves formed in the barrel of a syringe. This modifiedarrangement is particularly suitable for use with a syringe which is tobe loaded once only by pressure or suction filling.

As shown in FIG. 10, the finger 19 could be biased by a spring 22 toensure desired movement of the key 10 through the camway 11 if thesyringe is filled by means of pressure from a pressurised vial.

The syringe could be modified in such a way that the full dose must bedelivered in one continuous stroke. This would overcome the possibilityof unethical users trying to cause, for example, a 2 ml syringe todeliver 4 ×0.5 ml doses to four different patients. Thus the inner faceof the plunger housing 3 could be formed with castellations (instead ofthe serrations of FIG. 6). Then, with the incorporation of themodifications shown in FIGS. 9 and 10, if pressure on the plunger isreleased, the projecting webs 21 would engage with the castellations.Another possibility is to form the webs 21 from a metal or some otherhard material which again has a small degree of flexibility and which ispositioned and shaped in such a fashion as to dig into the inner sidewall of the plunger housing if pressure on the plunger is released.

A further possible modification would be to construct the plunger on apiston and coupling in such a way that after the final injection strokethe plunger can move towards the piston seal 7, if retracted anddepressed again so that, with a proper seal, the plunger would pierceand rupture the seal, thus rendering the syringe unusable.

It will be appreciated that any of the plunger and piston unitassemblies 2 illustrated in the drawings may be used with a conventionalsyringe barrel. Once the syringe has been used the assembly 2 will breakdown into its component parts, so that the syringe cannot then be reusedas it stands.

I claim:
 1. A syringe comprising a barrel housing both a piston and aplunger for moving the piston to enable a liquid dose to be drawn intoand ejected from a portion of the barrel, a coupling memberinterconnecting the piston and the plunger, and decoupling linkagesinterconnecting the coupling member to at least one of the piston andthe plunger such that the plunger is operatively disconnected from thepiston after the plunger has been retracted and subsequently depressed,a flange on the piston or the coupling member, and latches on the innerwall of the barrel which interact with the flange so that the flange isable to pass the latches before disconnection of the or each of thecoupling linkages but is unable to pass the latches upon attemptedwithdrawal of the plunger after such disconnection.
 2. A syringeaccording to claim 1 wherein the latches are in the form of inwardlyprojecting serrated ribs or inwardly spring-loaded arms.
 3. A syringeaccording to claim 1 wherein the parts of the or each decoupling linkagedefining the camway and the cam follower respectively are biased apartby a spring or other biasing means.
 4. A syringe according to claim 1wherein the plunger and piston are keyed together for rotationalmovement but are separable on retraction after disconnection of thedecoupling linkage.